Electrical fuses



Aug. 16, 1966 HlRoo ARIKAWA ETAL 3,267,238

v ELECTRICAL FUsEs Filed Aug. l?. 1964 UnitedStates Patent O Mice 3,267,238 ELECTRICAL FUSES Hiroo Arikawa, Tokyo, and Fumitake Akiyama, Yokohama-shi, Japan, assignors to Sony Corporation, Tokyo, Japan, a corporation of Japan Filed Aug. 17, 1964, Ser. No. 390,108 6 Claims. (Cl. Z110-123) This invention generally relates to electrical fuses andmore particularly relates to time-delay electrical fuses.

Time-delay electrical fuses have two major characteristics-one permitting a large overload rush or surge current to flow through the fuse withoutinterrupting or blowing the fuse and interrupting or blowing the fuse in response to relatively moderate constant current overloads. Such time-delay fuses are utilized to protect circuits for various types of motors, radio receivers, television receivers, and similar electrical means that have a large surge current flow when the power source connected thereto is switched on.` For example, in television receivers and the like, a surge current rea-ching as high as 20 times the fuse rating ows for 10-50 milliseconds before the 'receiver reaches normal operating conditi-ons and uses a relatively steady flow o-f current.

Therefore, it is an object of the present invention to provide an improved time-delay fuse having a fuse-link interconnected between two spaced terminals.

It is still another object of the present invention to provide a time-delay cartridgefuse.

It is still another object of the present invention to provide a time-delay fuse having a fuse link composed of at least twol different types of wires being twisted together and connected at their ends to two spaced terminals. t It is still another object of the present invention to provide a fuse link for an electric fuse wherein the link comprises a tungsten wire and a copper coated manganesenickel alloy wire twisted together and connected at their respective ends to the electrical Afuse spaced terminals.

It is still another object of the present invention to provide a cartridge fuse with a fuse link extending along the axis thereof and having a relatively straight silver coated tungsten wire attached at its ends to the spaced terminals and a copper coated manganese-nickel wire with 80 percent by weight of copper and the copper coated manganese wirelbeing helically wound around the silver coated tungsten wire for substantially the length thereof and attached at its ends to the spaced cartridge terminals.

t Other objects, features and advantages of the present invention will becomeapparent after a careful considerationof the following description and drawing wherein like reference numerals referred to like and corresponding parts. i

In the drawing:

FIGURE 1 is a partial end perspective view of a wire used to form a fuse link constructed in accordance with the principles of the present invention;

- FIGURE 2 is a partial end perspective view of another wire used to construct a fuse link constructed in accordance with the principles of the present invention;

FIGURE 3 is an elevational view illustrating a Ifuse link constructed in accordance with the principles of the present invention; and

FIGURE 4 is an electrical fuse constructed in accordance with the principles of the present invention.

As shown in the drawing:

An electrical fuse of the present invention is composed of fuse link interconnected at its ends to the spaced terminals of the fuse. The fuse link is formed with at least two fusible conductors that are twisted together and have their ends electrically connected to the spaced terminals Patented August 16, 1966 of the electrical fuse. One of the fusible conductors has a relatively low coeicient of thermal linear expansion and a relatively high electrical resistivity while the other fusible conductor has a relatively small electrical specific resistivity. Both of the fusible conductors are preferably capable of being drawn into wires.

Referring to FIGURE 1, there is illustrated a first fusible conductor comprising a tungsten wire 1 having a relatively thin layer of silver 3 plated thereon. The tungsten wire is preferred because it has a lrelatively low coeflicient of thermal expansion being on the order of 4X10r, relatively high thermal conductivity and electrical specific resistivity, and a suitable hardness and ductility such that it may be drawn to a predetermined size wire for various sized fuses. A thin coating of silver is plated on the tungsten wire and then the silver coated tungsten wire is subjected to heating and annealing processes in a hydrogen gas atmosphere.

Referring to FIGURE 2 there is illustrated a second fusible conductor 11 comprising a manganese-nickel alloy wire 2 with a copper coating 4 thereover and a relatively thin outersurface of `tin over the copper. The fusible conductor 11 is provided by covering .a manganese-nickel alloy core with copper tubing and then drawing the copper clad alloy core into a predetermined diameter copper coated manganese-nickel alloy wire being at least percent by weight of the copper. After the wire is drawn to a suitable diameter it is plated with tin to provide an outer protective coating 5 of increased moisture and oxidation resistance.

Referring to FIGURE 3, a fuse link 13 is provided by twisting or helically winding the copper coated manganese-nickel lalloy wire 12 around a relatively straight silver coated tungsten wire 10. The copper wire 12 is helically wound around substantially the entire length of the straight tungsten wire 10. This twisting interconnection between the tungsten and copper wires provides an unique time-delay fuse link 13 which blows or interrupts relatively instantaneously in response to a moderatelyl overloaded relatively steady current passing therethrough while also maintaining its integrity to allow passage therethrough of la large surge current between 10-20 times greater than the rated current of the fuse.

Referring to FIGURE 4, a cartridge fuse 9 of typical construction is illustrated. The cartridge fuse includes a glass or the like insulation tube 6, a pair of terminal end caps 7, 7 having concave end faces 8, 8 and being suitably attached to the ends of the insulation tube 6, and .a fuse link 13 electrically interconnecting the end terminals 7, 7. The fuse link 13 has its ends turned and soldered-to the end caps 7, 7 such that the fuse link 13 extends substantially axially within the cartridge fuse 9 and is spaced radially inwardly a predetermined distance from the inner walls of the tube 6. The thermal expansion of the fuse link 13 is provided such that the fuse link will not expand to touch the inner walls ofthe tube 6 upon the flow of current therethrough.

xample I A silver coated tungsten wire 1 of a diameter of 0.025 millimeters is prepared by drawing a predetermined length Vof tungsten wire 1 having a substantially uniform cross-section, plating the drawn wire with silver, and then subjecting the silver-plated tungsten wire to annealing in a hydrogen gas atmosphere. A copper coated manganesenickel alloy wire is prepared by drawing a predetermined length of copper coated manganese-nickel alloy core into a copper coated alloy wire having a substantially uniform cross-section, a 0.045 millimeter diameter and being at least 80 percent copper. The following table lists the relative percentages by weight of three copper coated manganese-nickel alloy wires used.

Contents of a 0.045 millimeter copper coated manganese-nickel alloy wire The above copper coated alloy wires are preferably plated with moisture and oxidation resistant ti'n coatings having approximately a 2n thickness.

The oxidation resistant copper coated manganese-nickel alloy wire is twisted -or helically wound around substantially the entire length of the relatively straight Isilver coated tungsten wire. The helically wound copper coated wire is approximately 3 centimeter long and is Wound around the tungsten wire with 120 pitches per centimeter to provide the fuse link 13 that has a rated current of 0.35 ampere. The fuse link is then enclosed in the glass tube 6 and suitably attached to the terminal caps 7, 7 by soldering the ends of the silver coated tungsten wire 10 and the ends of the copper coated manganese-nickel alloy wire 12 to the terminal caps 7, 7. The -fuse will withstand the` steady overload currents up to 1.4 times greater than the rated current and will blow within 10 seconds with steady overload currents being double the Irated current. Also, the fuse will allow a surge current 10-20 times greater than the rated current to ow therethrough without blowing, and specifically, the fuses set forth above did not blow within 10 milliseconds with a surge current that was 14 times greater than the rated current of 0.35 ampere.

It is of course yunderstood that the rated current values of the fuses are varied in accordance with the various factors related thereto such as the length and crossesectional dimensions of the -fusible conductors, the number of pitches in the twisted fusible conductor etc. Also, although the fusible conductors 10 and 12 were illustrated as being cylindrical wires, they, may be wires of any shape.

Further, it is understood that modifications land variations of the foregoing preferred exemplary embodiment of the invention may be effected without departing from the scope of the invention and it is intended that the scope of the invention be limited only by the hereunto appended lclaims.

We claim as our invention:

1. A time-delay fuse comprising:

a pair of spaced terminals,

. conducting means electrically connecting the terminals, said conducting means having at least two different fusible conductors,

one of said fusible conductors being a wire with a man ganese-nickel alloy core and a copper coating over the core and the copper coating being at least 80 percent by weight of the wire, and

said two fusible conductors being twisted together.

2. A time-delay fuse comprising:

a pair of spaced terminals,

conducting means electrically connecting the terminals,

said conducting means having at least two different fusible conductors,

one of said fusible conductors being a' wire with a manganese-nickel alloy core and a copper coating over the core and the copper coating being at least 80 percent by weight of the wire, the other fusible conductor being a silver coated tung- Y sten wire, and said two fusible conductors being twisted together.

3. A time-delay fuse comprising: a pair of spaced terminals, conducting means electrically connecting the terminals,

said conducting means having at least two different fusible conductors,

one of said fusible conductors being a Wire with a manganese-nickel alloy core and a copper coating over the core and the copper coating being at least percent by Weight of the wire,

the other fusible conductor being a silver coated tungsten wire,

one of said wires extending substantially in a straight line between said terminals, and

the other of said wires being helically wound around said one wire.

4. A time-delay fuse comprising:

a pair of spaced terminals,

conducting means electrically connecting the terminals,

`said conducting means hav-ing at least two different fusible conductors,

one of said fusible conductors being a wire with a manganese-nickel alloy core and a copper coating over the core and the copper coating being at least 80 percent by weight of the wire,

the Iother fusible conductor being a silver coated tungsten wire, v

the silver coated tungsten wire extending substantially in a straight line between said termina-ls, and

the copper coated wire being helically wound around the copper coated wire and extending substantially the length thereof.

5. A time-delay fuse comprising:

a pair of spaced terminals,

a relatively straight first fusible conductor electrically connecting said terminals,

a twisted second fusible conductor being helically wound around said first conductor and electrically connecting said terminals,

said first fusible conductor being a wire having a tungsten core and a silver coating on said tungsten core, and

said second fusible conductor wire having a manganesenickel alloy core, a copper coating on said alloy core being at least 80 percent by weight of the copper and core, and a thin tin outer layer on said copper coating whereby said fuse will maintain electrical connection between said terminals for ten milliseconds at least 10 times a rated current.

6. A time delay fuse comprising a pair of spaced terminals, a pair of conductors electrically connected to said terminals, one of said conductors being twisted about the other, one of said conductors being composed of a metal having a relatively low coeicient of thermal expansion on the order `of 4 106 and a relatively high resistivity, and the other of said conductors being composed of a metal having a lowelectrical resistivity.

References Cited by the Examiner UNITED STATES PATENTS 470,014 3/1892 Scott et al 200-135 919,696 4/1909 Cook 200-135 1,068,341 7/1913 Hope 200--135 FOREIGN PATENTS 69,599 2/ 1915 Austria. 10,082 8/ 1914 Great Britain. 233,752 5/ 1925 Great Britain. 586,586 3/1947 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

6. A TIME DELAY FUSE COMPRISING A PAIR OF SPACED TERMINALS, A PAIR OF CONDUCTORS ELECTRICALLY CONNECTED TO SAID TERMINALS, ONE OF SAID CONDUCTORS BEING TWISTED ABOUT THE OTHER, ONE OF SAID CONDUCTORS BEING COMPOSED OF A METAL HAVING A RELATIVELY LOW COEFFICIENT OF THERMAL EXPANSION ON THE ORDER OF 4X10**-6 AND A RELATIVELY HIGH RESISTIVITY, AND THE OTHER OF SAID CONDUCTORS BEING COMPOSED OF A METAL HAVING A LOW ELECTRICAL RESISTIVITY. 